The invention relates generally to a method and device for preparing container board for folding. In particular, the invention concerns providing a device for displacing in a non-destructive manner the corrugated material and the liner in a portion of the container board to form a curved indentation therein and a separate creasing tool for forming a line of weakness in the liner along the indentation.
Container board boxes are widely used for the packaging of multiple items, such as bottles, and heavier items, such as refrigerators, televisions, and other consumer goods. Container board boxes are commonly fabricated from a web of container board which has been slotted, creased, and cut into blanks. The blanks are then folded on the crease line and glued to form flattened box blanks. The box blanks are then formed into the final box shape by the packager to receive products therein.
Modern value-added package design and automated filling equipment demand that the boxes be dimensionally accurate. One of the main factors affecting the dimensional accuracy of container board boxes is the size of the box panels. Presently, box panel size is determined by mechanically scoring a crease line into the container board.
One such existing creasing device 110 is shown in FIG. 1 and includes a pair of shafts 112. A female ring 114 is mounted on a hub 116 located on one of the creasing/scoring shafts 112. A male ring 118 is mounted to a hub 120 located on the other creasing/scoring shaft 112. The female ring 114 and the male ring 118 form a nip for receiving a web of container board 124. The male ring 118 includes a male scoring bead 122 for compressing the container board 124 into the female ring 114.
The container board 124 comprises a corrugated medium 126 interposed between an inner liner board 128 and an outer liner board 130. The male scoring bead 122 forms a crease line 132 (best seen in FIG. 2) in the inner liner 128 and the corrugated medium 126 at the nip between the male and female rings 114 and 118. The crease line 132 separates the container board 124 into side-by-side panels, such as an inboard panel 134 and an outboard panel 136.
There is a critical value of nip pressure that must be maintained in order to produce a useful crease line 132. Too little nip pressure produces an undefined crease line, whereas too much pressure tends to cut or crack the liner paper of the liner boards 128 and 130.
After the crease line 132 is formed, the outboard panel 136 is urged down around the crease line 132 either by a rotating folding rod 138 or moving belt (not shown). By nature, folding a container board sheet requires the outer liner board 130 to stretch, the inner liner board 128 to contract, and the corrugating medium 126 to compress.
Due to the many variables encountered in the manufacture of container board boxes, such as liner and medium paper weights, moisture content, and recycled grades, the flutes of the corrugated medium 126 adjacent to the crease line 132 may be weaker than the crease line 132 itself and frequently causes the outboard panel 136 to fold about a xe2x80x9cfalsexe2x80x9d score line 140. These false score lines 140, also known as xe2x80x9crolling scoresxe2x80x9d, change the dimension of the panels 134 and 136 on either side of the false score 140, producing a container board box that is dimensionally not within specification. Since the dimensions of the panels are different from the design dimensions, the container blank forms a parallelogram when folded and not the intended rectangular shape. The false score lines 140 can occur at anytime during a production run of boxes and are very difficult to eliminate with normal machine set-up functions.
The present invention substantially eliminates the occurrences of xe2x80x9crolling scoresxe2x80x9d by displacing paper in a controlled non-destructive manner before the container board is creased to produce the necessary clearances required to permit accurate bending of the panels around the xe2x80x9ctruexe2x80x9d crease line.
The present invention includes a device for displacing in a non-destructive manner the corrugated medium and at least one of the liners in a portion of the board to form a curved indentation therein. A crease or line of weakness is then formed in the liner along the curved indentation of the board.
It is contemplated that the device can comprise a rotatably supported backing ring and a cooperating rotatably supported forming ring with a peripheral face having a curved profile. The container board is received between the nip formed between the peripheral faces of the forming and the backing rings. The curved profile of the forming ring cooperates with the peripheral face of the backing ring to displace the corrugated medium and at least one of the liners to form the curved indentation therein.
It is further contemplated that the device imparts to the container board a curved indentation having a parabolic shape.
In one form of the invention the profile of the peripheral face of the forming ring has a radius of about six inches (15.24 cm) and a width of about one inch (2.54 cm). The peripheral face of the backing ring has a substantially flat profile and is at least about two inches (5.08 cm) wide.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment as amplifying the best mode of carrying out the invention as presently perceived. The detailed description particularly refers to the accompanying drawings.